FIG. 1A is a diagram illustrating an example of a physical topology and an IP (Internet Protocol) topology in an optical network. In the optical network, the physical topology is formed by connections between OXCs (Optical Cross-Connect). Each OXC is connected to a router through a transponder. The OXC converts an optical signal and an electrical signal, an optical signal flows between the OXCs, and an electrical signal flows between the OXC and the router.
The transponder of the OXC and a port of the router for connection with the OXC can control on/off of the power. Therefore, a link between routers (optical direct path) is validated by turning on the transponder of the OXC and the connection port of the router. More specifically, the IP topology can be dynamically generated by dynamically turning on/off the links between the transponders of the OXCs and the connection ports of the routers. As for the connections between OXCs, on/off cannot be controlled.
In FIG. 1A, the IP topology is a topology connecting the points in a full mesh. A direct path linking a router #1 and a router #3 in the IP topology of FIG. 1A is a route through the router #1, an OXC #1, an OXC #2, an OXC #3, and the router #3 on the actual physical topology.
FIG. 1B is a diagram illustrating an example of light paths corresponding to IP links. In FIG. 1B, an IP topology 50 is formed on the physical topology illustrated in FIG. 1A. On the IP topology 50, a direct path is not formed between the router #1 and a router #4. Therefore, the paths between the router #1 and the router #4 are, for example, routes using an IP link between the router #1 and the router #3 and an IP link between the router #3 and the router #4, through the router #3. In this way, paths between two routers on the IP topology that go through another router will be called “multi-hop paths”, hereinafter.
The paths between the router #1 and the router #4 on the physical topology are also routes using a path between the router #1 and the router #3 and a path between the router #3 and the router #4. Therefore, the connection port of the router #1 and the transponder of the OXC #1 as well as the connection port of the router #4 and the transponder of the OXC #4 are turned on. Furthermore, in the router #3 and the OXC #3, the connection port and the transponder for the path between the router #1 and the router #3 as well as the connection port and the transponder for the path between the router #3 and the router #4 are turned on. In the routers and the OXCs, the correspondence between the connection ports, the transponders, and the linked routers can be changed by setting.